As it is well known by the technicians skilled in the art, hermetic reciprocating compressors comprise equipment able to compress a certain work fluid. Being applied normally in refrigeration systems, the hermetic reciprocating compressors are, therefore, able to compress any refrigerating fluid.
More particularly the compression of a work fluid, in a hermetic reciprocating compressor is brought about by the dynamic changes of volume of at least one pressure chamber, being such change in volume brought about by the reciprocating movement of a specific component inside the referred pressure chamber. Normally, the specific component able to reciprocate inside the pressure chamber is called a piston, and the pressure chamber is normally called compression cylinder.
In this sense, the reciprocating movement of the piston, inside the pressure chamber aligning to the synchronization of the valves of suction and discharge is able to draw the work fluid at reduced pressure, compress it and discharge it into any other system (normally, a refrigeration system) at high pressure.
In the specific case of reciprocating compressors, whether hermetic or not, the reciprocating movement of the piston is generated from the continuous movement of a rotating drive source, which is habitually comprised by an electric engine with a rotating shaft. To this end, the connection between the rotating shaft of the electric engine and the piston is brought about by a mechanical assembly comprised by an eccentric shaft and an extension rod (or connecting rod).
The eccentric shaft is coupled to the rotating shaft of the electric engine, and the extension rod is coupled both to the eccentric shaft and the piston. Thus, the rotation movement of the engine shaft is transformed into a reciprocating movement for the piston.
As it is also known to the technicians skilled in the art, the compression unit (integrated by the mobile elements of the compressor) for the hermetic reciprocating compressor is physically associated to the hermetic housing through the suspension structures.
The referred suspension structures of the compressors are always in technical development.
The reason for this is that the reciprocating movement of the piston, together with the movement of the rotating shaft of the electric engine, eventually generates vibrations and noises which should be, preferably, reduced before they reach the hermetic housing, and, therefore, the outside environment. Thus the technical evolution of the suspension structures of compressors is basically associated to the optimization of the reduction of vibration and noises.
In general, the suspensions of the compressors, independently of their type, are composed by two end stops and a semi-rigid or resilient element disposed between the referred end stops.
Normally, one of the end stops is anchored on the compression unit whereas the other end stop is anchored on the hermetic housing, the semi-rigid or resilient element being responsible for absorbing the vibrations and noises of the compression unit before they are spread to the hermetic housing.
The state of the art comprises a great variety of models of suspensions for compressors.
KR362853, for example, describes a suspension for a compressor composed by a pair of ball joints each one of which is fitted with a discoid projection and a cylindrical projection. In this realization, one of the ball joints is housed in a spherical cavity defined in the compression unity (in the compressor block) while the other ball joint is housed in a spherical cavity defined in the lower inside wall of the hermetic housing, the discoid and the cylindrical projections of both the joints facing each other. A spring is also provided between the referred ball joints, the ends of the referred spring being inserted between the said discoid and cylindrical projections. Apparently this kind of suspension allows, due to the ball joints, for a wider range of movements between the compression unit and the hermetic housing.
However, this kind of suspension—and the vast majority of compressor suspensions pertaining to the state of the art—has no provision of any type of protection of the end stops attached to the compression unit and to the hermetic housing (in this case, the ball joints), and if the compression unit undergoes an involuntary and sudden movement, common in mobile applications, there is a possibility that the said end stops bump into each other, reducing their lifetime. Therefore, the suspension described in KR362853—and the vast majority of compressor suspensions pertaining to the state of the art—do not present the fundamental conditions for the use of the hermetic reciprocating compressors for mobile application.
JP2010229833, for example describes a hermetic compressor that comprises suspension structures able to prevent the blocking of the spring disposed between the two end stops, besides reducing, theoretically, the level of the vibrations and noises between the compression unit and the hermetic housing with this end in view, the upper end stop (attached to the compression unit) is made up by a pin and a pin cover, the free end of the pin piercing the pin cover and projecting out and in the direction of the lower end stop (attached to the lower inside wall of the hermetic housing). Apparently, before the spring disposed between the two end stops is fully compressed (blocking state), the free end of the pin of the upper end stop contacts the top of the lower end stop.
However, this type of suspension does not provide any type of protection for the end stops attached to the compression unit and to the hermetic housing and, in the event of the compression unit presenting an involuntary and sudden movement, common in mobile applications there is a possibility of the said end stops bumping into each other, reducing their lifetime. Therefore, the suspension described in JP2010229833 does not present the fundamental conditions to make it able to be used in hermetic reciprocating compressors of mobile application.
KR200052152, for example, describes a compressor suspension especially destined to the absorption of eventual sudden shocks. To this end, the lower end stop (attached to the lower inside wall of the hermetic housing) is provided at the top with another spring. The referred spring has one end attached to the top of the lower end stop and the other free end facing the upper end stop. Thus, this kind of suspension, as opposed to the others, provides at least some protection for the end stops, for the case of a shock produced by the involuntary and sudden movements of the compression unit.
However, as it is known to the technicians skilled in the art, in mobile applications, the hermetic reciprocating compressors are also subject to small vibrations and noises its source related to the mobile application itself, as in automotive vehicles, for example. These small vibrations and noises, if not conveniently isolated, resonate inside the hermetic housing, being amplified to harmful and unpleasant levels.
Therefore, the suspension described in KR2005052152, although providing protection for the end stops, does not provide for any kind of absorption of small vibrations and noises between its body and the hermetic housing of the compressor, not providing, therefore, the essential conditions for its use in hermetic reciprocating compressors for mobile application.
U.S. Pat. No. 7,722,335, on the other side, describes a suspension specifically directed to linear compressors that, apparently, have means for the absorption of small vibrations and noises between its lower end stop and its housing but does not provide any kind of protection related to the eventual shock between the upper end stop and the lower end stop.
As has been described and claimed in U.S. Pat. No. 7,722,335, the suspension is integrated by an upper end stop (attached to the compression unit), by a lower end stop (attached to the lower inside wall of the hermetic housing) and a spring disposed between the two end stops.
The upper end stop has a simple construction, being defined by a monoblock body able do house one of the spring ends.
The lower end stop has a more complex construction, being defined by a pin, a tubular damping sleeve and an outside cover. The pin is directly attached to the housing leaving its top, in the form of a “T”, totally free. The outside cover, intended to house the other spring end, has an annular structure with the outside profile essentially in the form of a truncated cone, while the inside profile is essentially cylindrical. A tubular damping sleeve disposed between the pin and the outside cover further defines a lower deformation to prevent the physical contact between the outside cover and the housing and an upper deformation to prevent the contact of the outside cover with the pin.
Therefore, and for all effects, the outside cover is physically isolated from the pin and from the housing. Consequently, small vibrations and noises (from an outside source) impacted on the compressor housing are absorbed by the tubular damping sleeve, before being led to the outside cover. However, if there is a sudden movement in the compression unit in relation to the housing (also coming from an inside source), it should be observed that the top of the upper end stop will bump against the pin of the lower end stop, damaging both components, and eventually, damaging the compressor housing itself.
Therefore, the suspension described in U.S. Pat. No. 7,722,335, though providing means for the absorption of small vibrations and noises, lacks the protection for the end stops, lacking, therefore, the essential conditions for its use in hermetic reciprocating compressors for mobile application.
The presence of the technical shortcomings of the state of the art described above gave rise to the present invention.